Control of insect vectors is an important tool in preventing the spread of viruses and parasites. In recent years the use of biological control methods, particularly microbial control of vectors and pests has gained popularity. Live insect viruses have been developed commercially as viral insecticides and two have already been approved for use in destroying pests. Attempts are also being made to kill mosquito vectors by using specific mosquito-pathogenic viruses. We are now proposing a new approach to obtain insect-pathogenic viruses: the use of mammalian cell cultures that can support baculovirus (insect polyhedrosis) multiplication. Following our successful production of baculovirus polyhedra and free intranuclear virions in a diploid mammalian cell line in vitro, a study will be undertaken with several baculoviruses affecting mosquito vectors and pests, using virus obtained from mammalian cell lines. Since these cell lines are routinely monitored for freedom from bacterial, rickettsial, mycoplasma, symbiote and virus contaminations, the new approach will provide a standardized means for the production of virus inocula, permitting product control not previously possible for baculoviruses. The use of mammalian cell production of baculovirus is expected to have practical applications for large-scale production of viral insecticides.